The land on the left side of the boundary in this picture belongs to South Korea while on the right side it belongs to North Korea.

When Japan surrendered in August 1945, the 38th parallel was established as the boundary between Soviet and American occupation zones. This parallel divides the Korean peninsula roughly in the middle. In 1948, this parallel became the boundary between the Democratic People's Republic of Korea (North Korea) and the Republic of Korea (South Korea), both of which claim to be the government of the whole of Korea. On 25 June 1950, after a series of cross-border raids and gunfire from both the Northern and the Southern sides, the North Korean Army crossed the parallel and invaded South Korea. This sparked a United Nations resolution against the aggression and the Korean War, with United Nations troops (mostly Americans) helping to defend South Korea.[2]

After the Armistice ended the Korean War in 1953, a new border was established based on the territory that each side held at that point. This Military Demarcation Line is surrounded by a Demilitarized Zone. It crosses the 38th parallel, from the southwest to the northeast. The new border is still often described as the 38th parallel, but this is not accurate.